1. Field of the Invention
The present invention relates to an image capturing apparatus and a control method for the image capturing apparatus, and particularly relates to an image capturing apparatus that is capable of recording moving images and a control method for the image capturing apparatus.
2. Description of the Related Art
Conventionally, image capturing apparatuses that have an automatic focus detection (AF) function and are capable of capturing moving images are known. For example, Japanese Patent Laid-Open No. 02-140074 discloses a video camera having an automatic focus detection (contrast-detection type AF) function that employs so-called hill-climbing control that successively drives a focus detection lens based on contrast components of an object image. In Japanese Patent Laid-Open No. 02-140074, after the focus detection lens is stopped at a focusing position, when the need to perform focus detection once more arises, the focus detection lens is first driven back and forth to detect a focusing direction, and then hill-climbing control is performed while driving the focus detection lens in the detected direction.
As an automatic focus detection method, in addition to the aforementioned contrast-detection type AF, for example, phase-difference detection type AF that determines a non-focusing distance (defocus amount) using a phase difference between images formed by light beams passing through different regions of an exit pupil of a lens also is commonly used.
Moreover, a combination of the contrast-detection type AF and the phase-difference detection type AF has also been proposed. For example, Japanese Patent Laid-Open No. 2007-248782 proposes a focus detecting apparatus that performs focus detection using the contrast-detection type AF in the case where the exit pupil is reduced in size by an aperture mechanism of a lens and therefore the phase-difference detection type AF cannot be used in a currently set focus detection region.
It has hitherto been common that the contrast-detection type AF detects focus information (contrast components) from a captured image, and the phase-difference detection type AF detects focus information (a pair of images) using a detecting device separate from an image sensor. However, an image capturing apparatus having an image sensor in which pixels for detecting a phase difference are formed and performing the contrast-detection type AF and the phase-difference detection type AF using an output from the image sensor has also been proposed (Japanese Patent Laid-Open No. 2007-65330).
Conventionally, small digital cameras in which an electronic viewfinder (EVF) is mainly used usually had a moving image shooting function, but many lens-interchangeable type digital cameras did not have the moving image shooting function or were not able to perform automatic focus detection during shooting of a moving image. However, in recent years, an increasing number of lens-interchangeable type digital cameras have been provided with a so-called live view function that is similar to the EVF, and at the same time, the moving image shooting function has also become standard.
In this manner, digital (still) cameras and digital video cameras are becoming functionally more similar to each other. However, there is still a great difference in terms of the automatic focus detection method. Video cameras are primarily intended to shoot moving images and therefore perform automatic focus detection on the assumption that the focusing distance fluctuates. Specifically, even after the focus has been detected, video cameras perform detection of a focusing direction by continuously moving (wobbling) the focus detection lens back and forth within a minute range (a range that does not significantly affect a moving image to be shot) around the focusing position. For this reason, a photographic lens that supports wobbling is used as well.
In contrast, digital still cameras are primarily intended to shoot still images, and therefore, in the case where the focus has been detected, the focus detection lens usually is stopped at that focusing position. Accordingly, many photographic lenses for use in digital still cameras do not support driving within a minute range, such as wobbling. For this reason, if driving for detection of the focusing direction like wobbling is performed once the focus has been detected, the resulting drive distance becomes long and affects the image quality of a captured image. In the case of fixed lens type digital still cameras, this problem is expected to be solved in the near future because it is envisaged that fixed lens type digital still cameras equipped with a lens that allows for wobbling will increase in the future. However, as for lens-interchangeable type digital still cameras, it is unlikely that all the available photographic lenses (interchangeable lenses) will support wobbling in the near future, and so it is envisaged that the problem will remain for some time.